A number of epidemiological studies have shown that higher than normal circulating levels of IGF-1 are associated with increased risk for several common cancers, including breast (Hankinson et al, Lancet 1998. 351:1393-6), prostate (Chan et al, Science. 1998. 279:563-6), lung (Yu et al, J. Natl. Cancer Inst. 1999. 91:151-6) and colorectal cancers (Ma et al, J. Natl. Cancer Inst. 1999. 91:620-5). Elevated circulating levels of IGF-2 also have been shown to be associated with increases risk for endometrial cancer (Jonathan et al, Cancer Biomarker & Prevention. 2004. 13:748-52). On the contrary, inverse correlation was observed with elevated levels of one of the IGF binding proteins, IGF-BP3, and cancer risk. Furthermore, elevated levels of IGFs have also been found in cancer patients (Peyrat et al Eur. J. Cancer. 1993. 351:1393-6; Jonathan et al, Cancer Biomarker & Prevention. 2004. 13:748-52).
IGF system plays an important role in regulating cell proliferation, differentiation, apoptosis and transformation (Jones et al, Endocrinology Rev. 1995. 16:3-34). The IGF system comprises of two types of unrelated receptors, the insulin like growth factor receptor 1 (IGF-1R; CD221) and insulin like growth factor receptor 2 (IGF-2R; CD222); two ligands, insulin like growth factor 1 (IGF-1 and IGF-2); several IGF binding proteins (IGFBP-1 to IGFBP-6). In addition, a large group of IGFBP proteases (e.g.: caspases, metalloproteinases, prostate-specific antigen) hydrolyze IGF bound IGFBP to release free IGFs, which then interact with IGF-1R and IGF-2R. The IGF system is also intimately connected to insulin and insulin receptor (InsR) (Moschos et al. Oncology 2002. 63:317-32; Baserga et al., Int J. Cancer. 2003. 107:873-77; Pollak et al., Nature Reviews Cancer. 2004. 4:505-516).
In a cancer cell, receptor tyrosine kinases (TK) play important role in connecting the extra-cellular tumor microenvironment to the intracellular signaling pathways that control diverse cellular functions, such as, cell division cycle, survival, apoptosis, gene expression, cytoskeletal architecture, cell adhesion, and cell migration. As the mechanisms controlling cell signaling are better understood, therapeutic strategies of disrupting one or more of these cellular functions could be developed by targeting at the level of ligand binding, receptor expression/recycling, receptor activation and the proteins involved in the signaling events (Hanahan and Weinberg, Cell 2000. 100:57-70).
The type I insulin like growth factor receptor (IGF-1R, CD221) belongs to receptor tyrosine kinase (RTK) family, (Ullrich et al., Cell. 1990, 61:203-12). IGF-1R is widely expressed and its ligands, IGF-1 and IGF-2 play a significant role in pre- and post-natal development, growth hormone responsiveness, cell transformation, survival, and have been implicated in the acquisition of an invasive and metastatic tumor phenotype (Baserga, Cell. 1994. 79:927-30; Baserga et al., Exp. Cell Res. 1999. 253:1-6, Baserga et al., Int J. Cancer. 2003. 107:873-77). Immunohistochemical studies have shown that a number of human tumors express higher levels of IGF-1R.
The molecular architecture of IGF-1R comprises, two extra-cellular α subunits (130-135 kD) and two membrane spanning β subunits (95 kD) that contain the cytoplasmic catalytic kinase domain. IGF-1R, like the insulin receptor (InsR), differs from other RTK family members by having covalent dimeric (α2β2) structures. Structurally, IGF-1R is highly related to InsR (Pierre De Meyts and Whittaker, Nature Reviews Drug Discovery. 2002, 1: 769-83). IGF-1R contains 84% sequence identity to InsR at the kinase domain, whereas the juxta-membrane and the c-terminal regions share 61% and 44% sequence identity, respectively (Ulrich et al., EMBO J., 1986, 5:2503-12; Blakesley et al., Cytokine Growth Factor Rev., 1996. 7:153-56).
The IGF-1 and IGF-2 are the two activating ligands of IGF-1R. The binding of IGF-1 and IGF-2 to the α chain induces conformational changes that result in auto-phosphorylation of each β-chain at specific tyrosine residues, converting the receptor from unphoshorylated state to the active state. The activation of three tyrosine residues in the activation loop (Tyr residues at 1131, 1135 and 1136) of the kinase domain leads to increase in catalytic activity that triggers docking and phosphorylation of the substrates such as IRS-1 and Shc adaptor proteins. Activation of these substrates leads to phosphorylation of additional proteins involved in the signaling cascade of survival (PI3K, AKT, TOR, S6) and/or proliferation (mitogen-activated protein kinase, p42/p44) (Pollak et al., Nature Reviews Cancer. 2004. 4:505-516; Baserga et al., Biochem Biophys Act. 1997. 1332:F105-F126; Baserga et al, Int. J. Cancer. 2003. 107:873-77).
Despite the high degree of homology between IGF-1R and InsR, evidence suggests that the two receptors have distinct biological roles; InsR is a key regulator of physiological functions such as glucose transport and biosynthesis of glycogen and fat, whereas the IGF-1R is a potent regulator of cell growth and differentiation. In contrast to InsR, IGF-1R is ubiquitously expressed in tissues where it plays a role in tissue growth, under the control of growth hormone (GH), which modulates IGF-1. Although IGF-1R activation has been shown to promote normal cell growth, experimental evidence suggests that IGF-1R is not an absolute requirement (Baserga et al, Exp Cell Res. 1999. 253:1-6; Baserga et al, Int. J. Cancer. 2003. 107:873-77).
IGFs play a crucial role in regulating cell proliferation, differentiation and apoptosis. Inhibition of IGF-1R mediated signaling has been shown to reduce tumor growth rate, increase apoptosis, increase killing of tumors by chemotherapy and other molecular target therapies (reviewed in Pollak et al., Nature Reviews Cancer. 2004. 4:505-516; Zhang et al., Breast Cancer Res. 2000. 2:170-75; Chakravarti et al, Cancer Res. 2002. 62:200-07).
Experimental approaches undertaken to inhibit IGF-1R function in tumors have provided encouraging but limited success, and their effectiveness in treating cancer is yet to be determined in the clinic. The experimental approaches include; antibodies to IGF-1R (Kull et al., J. Biol. Chem. 1983, 258:6561-66; Kalebic et al., Cancer Res. 1994. 54:5531-4), neutralizing antibodies to IGF-1 or IGF-2 (Fang et al, Mol. Cancer Therapy. 2006. 5:114-20; Miyamoto et al, Clin. Cancer Res. 2005, 11:3494-502), small-molecule tyrosine kinase inhibitors (Garcia-Escheverria et al, Cancer Cell. 2004. 5:231-9; Scotlandi et al, Cancer Res. 2005. 65:3868-76), antisense oligonucleotides (Shapiro et al, J. Clin. Invest. 1994. 94:1235-42; Wraight et al. Nature Biotech. 2000. 18:521-26; Scotlandi et al, Cancer Gene Therapy. 2002. 9:296-07), dominant-negative mutants of IGF-1R (Prager et al, Proc. Natl. Acad. Sci. 1994, 91:2181-85; Kalebic et al., Int. J. Cancer 1998. 76:223-7; Scotlandi et al., Int J. Cancer. 2002:101:11-6), analogues of the IGF ligand (Pietrzkowski et al, Mol. Cell. Biol. 1992. 12:3883-89), recombinant IGF binding proteins (Yee et al. Cell growth Differ. 1994. 5:73-77; Van Den Berg et al, Eur. J. Cancer. 1997, 33:1108-1113; Jerome et al AACR 2004, Abstract #5334), antagonists of GH-releasing hormone, GHRH (Szereday et al, Cancer Res. 2003. 63:7913-19; Letsh et al, Proc Natl. Acad. Sci. USA. 2003. 100:1250-55) and GH (Kopchick et al, 2002. Endocr. Rev. 23, 623-46).
The ability of an antibody to inhibit IGF-1R function was first demonstrated with a mouse monoclonal antibody (α-IR3) targeting an unknown epitope in the α subunit of IGF-1R (Kull et al., J. Biol. Chem. 1983, 258:6561-66). Subsequently other antibodies developed to the α subunit of IGF-1R have been shown to inhibit IGF-1R function to varying degrees in different experimental cancer models (Maloney et al. Cancer Res. 2003. 63: 5073-83; Burtrum et al, Cancer Res. 2003. 63:8912-21; Sachdev D et al, Cancer Res. 2003. 63, 627-35; Cohen et al, Clin. Cancer Res. 2005. 11:3065-74; Goetsch et al, Intl. J. Cancer. 2005. 113:316-28. Lu et al, J. Biol. Chem. 2004. 280:19665-72).
In a cancer cell, in addition to pro-survival and proliferative signaling, activation of IGF-1R has also been shown to be involved in motility and invasion (Ress et al., Oncogene 2001. 20:490-00, Nolan et al, Int. J. Cancer. 1997.72:828-34, Stracke et al, J. Biol. Chem. 1989. 264:21544-49; Jackson et al, Oncogene, 2001. 20:7318-25).
Tumor cells have been shown to produce one or more of the components of the IGF system (IGF-1, IGF-2, IGF-1R, IGF-2R and IGF-BPs). Although in vitro studies have indicated that tumors can produce IGF-1 or IGF-2, translational studies indicate that IGF-2 is the more relevant and commonly expressed IGF in the tumors. This is due to loss of imprinting (LOI) of the silenced IGF-2 allele in the tumor by epigenetic alterations, resulting in biallelic expression of the IGF-2 gene (Fienberg et al., Nat. Rev. Cancer 2004. 4:143-53; Giovannucci et al, Horm. Metab. Res. 2003. 35:694-04; De Souza et al, FASEB J. et al, 1997. 11:60-7). This in turn results in increased IGF-2 supply to cancer cells and to the microenvironment supporting tumor growth.
IGF-1R sensitive tumors receive receptor activation signals of IGF-1 from the circulation (liver produced) and IGF-2 from the tumor, and thus approaches aimed at disrupting the biological activity mediated by both IGF-1 and IGF-2 should provide a better anti-tumor response. Therefore, anti-IGF-1R antibody methods that effectively block the biological functions mediated by both IGF-1 and IGF-2 may provide an improved efficacy over other approaches that do not efficiently block the biological functions of both IGF-1 and IGF-2 mediated IGF-1R signaling in tumor microenvironment.
With regard to safety, IGF-1R is ubiquitously expressed and thus antibodies targeting IGF-1R should have minimal or no effector functions to avoid toxicities resulting from ADCC and CDC activities in normal tissues. One possibility of developing such antibodies is to have the non-glycosylated form of the human gamma 4 Fc region, which does not mediate ADCC or CDC functions.
IGF-1R is involved in oncogene mediated cellular transformation.
IGF/IGF-1R activation mediates mitogenic and pro-survival signaling in cancer cell.
IGF-1R activation also promotes cell motility and metastasis.
IGF-1R is over expressed in many cancers.
Individuals with higher than normal circulating IGF levels have increased risk for developing cancer.
Increased plasma levels of IGF 1 & 2 found in many cancer patients.
Human tumors produce IGF-2 as an autocrine growth factor.
Inhibition of tumor growth has been demonstrated as single agent and in combination with chemotherapeutic and biological agents.
There remains a need in the art for IGF-1R antibodies with different or improved binding, efficacy, and safety characteristics for the treatment of various neoplastic diseases including cancer and metastases thereof.